1. Field of the Invention
The present invention relates to a liquid crystal display device, and more particularly, to a transflective liquid crystal display device including both a reflection display portion and a transmission display portion and a method of manufacturing the transflective liquid crystal display device.
2. Description of the Related Art
A liquid crystal display device has advantages such as thinness, light-weight, and low power consumption, compared with a cathode ray tube (CRT) which has been a mainstream of a display device conventionally, and the application of the liquid crystal display device has been enlarged as a display device for various electronic appliances. Among them, in a display device for a portable information appliance, there is a demand for the enhancement of visibility in various environments including indoor places and dark places with no light source present outside and places with high illuminance such as outdoor places under the clear sky, and a transflective liquid crystal display device including a transmission display portion and a reflection display portion in one pixel has come to be used widely.
In a transflective liquid crystal display device, the brightness is constant irrespective of an environment due to the use of a backlight in a transmission display portion, and hence a satisfactory display is obtained in relatively dark environments including indoor places to dark rooms. On the other hand, in a reflection display portion, the contrast is constant irrespective of the lightness of an outside since light from an outside is reflected by a reflective plate contained in the device to perform a display, and hence a satisfactory display is obtained in relatively light environments including outdoor places under the clear sky to indoor places.
On the other hand, as a liquid crystal display device with a large viewing angle, a liquid crystal display device of an in-plane switching (IPS) system has been known conventionally. However, when the IPS system is applied to a transflective liquid crystal display device, there arises a problem in that a black display is not obtained in a reflection portion. In order to solve this problem, JP 2006-184325 A realizes a reflection type display and a transmission type display by containing a polarizing layer.
Further, JP 2006-171723 A describes a transflective liquid crystal display device in a twisted nematic (TN) mode. Even in this transflective liquid crystal display device, both a reflection display and a transmission display are realized by containing a polarizing layer.
The polarizing layers contained in the devices in JP 2006-184325 A and JP 2006-171723 A are formed by applying a coating liquid containing a lyotropic liquid crystal as described in Japanese Patent Translation Publication No. 8-511109 as a polarizing material, followed by curing.
Table 1 of JP 2006-171723 A describes optical properties of a thin crystal film (TCF) manufactured by Optiva Inc., which is a solution made of a chromonic liquid crystal, and a dichroic ratio thereof (D=ln(perpendicular transmittance)/ln(parallel transmittance)) is calculated from the optical properties to be about 3 to 6. Further, the dichroic ratio of a polarizing film described in Table 1 of Japanese Patent Translation Publication No. Hei 8-511109 is 7 to 23. On the other hand, a commercially available polarizing film using iodine (polarizing film SEG1425DU, manufactured by Nitto Denko Corporation) has a dichroic ratio of 78, and a general commercially available polarizing film using iodine has a dichroic ratio of 70 to 80. Thus, an organic colorant film has much poor dichroic ratio, compared with that using iodine.
In a polarizing player to be contained in a transflective liquid crystal display device, the enhancement of a contrast ratio can be expected as a dichroic ratio becomes larger, and hence there is a demand for further enhancement of properties of a polarizing film in order to enhance image quality.